This invention relates to the field of wide bandwidth resistors, particularly as used in negative feedback amplifiers, and more particularly to thick film, deposited resistors in a conformation providing broad bandwidth along with high signal-to-noise ratio.
In an application such as a negative feedback amplifier where broad bandwidth is required, a fraction of the amplifier output is added to the input in phase opposition. When properly done, the amplification becomes substantially independent of the amplifier characteristics, the non-linear distortion produced in the amplifier is reduced, and the signal-to-noise ratio is greatly improved.
Negative feedback amplifiers as customarily used may be limited in bandwidth by the characteristics of the feedback resistor, since there is zero phase shift only in the frequency range for which the resistor remains purely resistive. With discrete resistors or known deposited resistors, high frequency rolloff is a limiting factor because of feedback capacitance and distributed capacity to ground.
In certain applications, it may be required to amplify very small currents coming from a high impedance source, such as 200 nanoamperes and 100 megohms. The feedback resistor provides a low input impedance for the amplifier so that the source capacitance will not limit the bandwidth. A high value resistor is required because of the small signal current.